It was, as a country song was to put it, the day "the world stopped turning"; 9/11 was not in the Stalingrad or Rwanda league in terms of casualties, but this did not dent its Earth-shattering impact. As the twin towers tumbled in full view of the world, the American homeland felt exposed as never before. A headlong rush into two wars followed, and all manner of unthinkable things began to be thought. These were times, the Bush administration decided, that demanded rendition, an attempted redefinition of torture, military tribunals, and the first steps towards the programme of universal surveillance of blameless citizens that Edward Snowden exposed last year.

There was also some quickfire rethinking to deal with the more proximate cause of a catastrophe unleashed by hijacked planes: stronger cabin doors, armed air marshals and the ban on razor blades in hand luggage. Some such steps may have been overdone; others were plainly sensible. One of the most coolly practical suggestions in these hot-headed times was to re-engineer transponders – the devices that broadcast an aircraft's whereabouts – so they could no longer be disabled. The about-turn towards New York of planes headed for Los Angeles might have been detected if the 9/11 hijackers had been unable to switch off the system; a prosaic tweak to prevent this could, perhaps, have saved thousands of souls.

But as the world again watches, bewildered, another aircraft's tragic veer away from its metaphorical tracks, Gregg Easterbrook, an expert who analysed the role of the communications shut-down on 9/11, has written in the New York Times that the morbid mystery of Malaysia Airlines Flight 370 was very possibly also enabled by the facility of someone in the craft to disable the transponder.

So much of flying is automated today that it is astonishing there should be any argument for a discretionary manual "off switch" for a something which should always be on when airborne. Yes, signals could get disrupted in those (older, smaller) airports that still lack the equipment to discount messages that come from planes on the runway. But even before every airport is modernised, the onboard kit could be refined so that it stops sending out signals on the ground. Neither end of MH370's Kuala Lumpur-Beijing journey between two major hubs should have necessitated any switching off; and yet it appears possible that somebody may have disabled not only the transponder, but also the aircraft communications addressing and reporting system.

The anguished wait of relatives, some threatening hunger strike, will be made harder by a sense that this is a tragedy that could have been prevented. If only the same frenzied post-9/11 energy absorbed in learning the wrong lessons had been applied to the right ones.